Status Report on PERC

Full text: Important open questions of particle physics and cosmology can be addressed with precision measurements in neutron beta decay. Main emphasis lies on the search for evidence of possible extensions to the Standard Model and searches for new symmetry concepts. In general, these measurements are complementary to direct searches in high-energy physics. Observables in neutron decay are abundant: Besides the neutron lifetime, angular correlations involving the neutron spin as well as momenta and spins of the emitted particles are characterized by individual coefficients. These coefficients can be related to the underlying coupling strengths of the weak interaction, including yet unobserved ones. Each coefficient in turn relates to an underlying broken symmetry. With the new facility PERC (http://www.physi.uni-heidelberg.de/Forschung/ANP/PERC/collaboration.php) several symmetry tests based on neutron decay data become accessible. PERC (Proton Electron Radiation Channel) is a novel source of neutron decay products: these are collected by a strong longitudinal magnetic eld of 1.5 T directly from inside a neutron guide. This combination provides highest phase space density of decay products. A magnetic mirror of up to 6 T serves to perform precise cuts in phase space, reducing related systematic errors. Altogether, the sensitivity of neutron decay studies will be improved by one order of magnitude. The new beam station PERC is currently under development by an international collaboration and will be installed at the FRM II in Garching, Germany. Besides the physics motivation, the concept, sensitivity, applications, and status of PERC are presented in this talk. (author)